Yes this would be useful. Occasionally I find there's no better source for high resolution art with some albums than the website of the artist that designed the cover. For example the site of Peter Saville.

Does anyone happen to know of a reliable source for Hi-Res [500x500+] album art? I've had hit and miss luck with tools that use amazon and google. Anything else to try?

Amazon has the largest consistent album art size, in my experience. In addition to the official store album art, the site allows users to upload their own, resulting in a few hi res specimens. Lossless album archives on P2P networks usually include scans. And there's also Google's image search.

iTunes (if you've got an iTunes account) has ~600 x 600 album art which is usually of excellent quality. Every now and again they've got some crappy ones. In that case, I check out Amazon.com and Google's image search.

iTunes (if you've got an iTunes account) has ~600 x 600 album art which is usually of excellent quality. Every now and again they've got some crappy ones. In that case, I check out Amazon.com and Google's image search.

Has anyone looked into integrating the itunes albumart functionality into a tool external to itunes? Would this even be possible?

I believe that Album Art Downloader has been mentioned in various places here before. It searches most sources for album art and displays them all, allowing you to sort by size and more. Generally, it works well for me.

Another place that has good 500x500 is buy.com. You have to mess with the site a little bit to be able to save the larger art though. Example. On this page you would click enlarge image, but when you try to right click on the image to save, it shrinks back down. To save it, right click on the enlarge image link, select Copy Link Location, then paste it into your address bar.